The present invention is directed to a method for producing a silicon boronitride layer having a dielectric constant .epsilon. of less than 4 .epsilon..sub.o by chemical vapor deposition in an alternating electromagnetic field.
Dielectric layers are required for intermetallization layers and final passivation layers in VLSI semiconductor circuits. These dielectric layers should exhibit low dielectric constants, good insulation and blocking properties, and have high break down strengths. The dielectric layers should also exhibit an optimally conformal step coverage of the layers lying therebeIow and should not have a hygroscopic effect.
In recent years, silicon nitride, deposited through plasma enhanced chemical vapor deposition methods (PECVD), has been increasingly utilized as a dielectric layer. In this respect, silicon nitride has replaced phosphorosilicate glass, which exhibits the unfavorable property of hygroscopicity. The silicon nitride layers provide good insulating properties and barrier properties against humidity and alkali ions. Moreover, siIicon nitride layers exhibit good step coverage and a high break down strength.
But, despite the advantages provided by the silicon nitride layers, the dielectric constant of these layers is relatively high (.epsilon.=7 .epsilon..sub.o), compared to that of phosphorosilicate glass or other silicon oxide layers (.epsilon.=4 .epsilon..sub.o). The relatively high dielectric constant results in parasitic leakage currents and relatively great delays in the transmission time between individual components. The articles by M. Maeda and Y. Arita, in the Journal of Applied Physics, Vol. 53, 1982, pages 6852ff and K. M. Mar and G. M. Samuelson, in Solid State TechnologY, Vol. 23, 9810, pages 137ff, provide a detailed discussion of this problem.
Boronitride layers are known that can be deposited by atmospheric pressure chemical vapor deposition (APCVD). The boronitride layers are chemically inert and temperature stable. Moreover, they have a low dielectric constant of .epsilon.=2.7 .epsilon..sub.o. However, boronitride layers are not stable with respect to atmospheric humidity, specifically in high-boron films. Discussions on investigations with respect to the APCVD deposition of boronitride layers are set forth in, for example, articles by M. Rand and J. F. Roberts in the Journal of the Electrochemical Society, Vol. 115, 1968, pages 423ff and S. B. Hyder and T. O. Yep in the Journal of the Electrochemical Society, Vol. 123, 1976, pages 1721ff.
According to Patent Abstracts of Japan, Vol. 9, No. 126 E 318, 1985, a ring-shaped molecule B.sub.3 N.sub.3 H.sub.6 can be used as an initial substance. In the alternative, according to W. Schmolla and H. Hartnagel in Solid State Electronics, Vol. 26, No. 10, 1983, pp. 931 ff , B.sub.3 N.sub.3 H.sub.3 (CH.sub.3) .sub.3, that is likewise a ring-shaped molecule, can be used as an initial substance.
In order to improve the moisture resistance of boronitride films, M. Maeda and T. Malino in the Japanese Journal of Applied Physics, Vol. 26, No. 5, 1987, pages 660-665 proposed a mixed nitride of silicon boronitride (SiBN). By utilizing what is referred to as a parallel plate PECVD reactor, utilizing a gas mixture composed of SiH.sub.4, B.sub.2 H.sub.6, NH.sub.3, and Ar, this amorphous silicon boronitride is deposited. However, the method requires the installation of gas feeds and that therefore result in a complicated structure, wherein the composition of the gas mixture is difficult to control.